HUD/DOE Pamphlet at BuildingScience.com
Buildingscience.com has a HUD/DOE pamphlet they authored on their web site. I haven’t seen this been discussed, so maybe it’s new. Looks like the basement insulation article got subsumed into it:
http://www.buildingscience.com/resources/mold/Read_This_Before_You_Design_Build_or_Renovate.pdf
If you don’t want to read all 56 pages, my reading of the executive summary is
NO VAPOR BARRIERS!
XPS in thicknesses of no more than 1″ for walls, 3/4″ for floors, to facilitate drying.
I also don’t think they like stud bays filled with closed cell foam. In general cells, batts or open cell foam (incl EPS) preferred.
On page 20 they talk about “foil-faced foam ‘flame-spread’ and ‘smoke-developed’ for exposed interiors.” Can anyone put a brand name on that? I never heard of such a thing.
Replies
I belive that some of the foil face poly iscynates are so rated.
Not true Taylor. On page 15 is a drawing of the wall that I prefer to use and it does indeed include a vapor barrier. We are moving away from interior vapor barriers in cold climates that have AC use in the summer if that is what you meant to say.
Ray, it is the discussion of drying on page 23 in particular that I was reacting to. They are really advising against poly VBs except in very cold environments.... but vapor retarders (whatever that is) still advisable....
This is copied from the BSC website.
Vapor Impermeable: Materials with a permeance of 0.1 perm or less (rubber membranes, polyethylene film, glass, aluminum foil)
Vapor Permeable: Materials with a permeance of greater than 10 perms (housewraps, building papers)
Vapor Retarder: A vapor retarder is the element that is designed and installed in an assembly to retard the movement of water by vapor diffusion. There are several classes of vapor retarders:
The test procedure for classifying vapor retarders is ASTM E-96 Test Method A — the desiccant or dry cup method.
Vapor Semi-Impermeable: Materials with a permeance of 1.0 perm or less and greater than 0.1 perm (oil-based paints, most vinyl coverings)
Vapor Semi-Permeable: Materials with a permeance of 10 perms or less and greater than 1.0 perm (plywood, OSB, most latex-based paints)
My version of the executive summary is: The whole 56 page booklet is an executive summary. Read it, understand it, then apply what is applicable for your house, in your climate. Investigate those designs further with the starting points that the executive summary provided.